1. Field of the Invention
This invention relates to determining the trigonometric functions of an input angle, and more particularly to reducing the hardware requirement of the above determination by dividing the input angle into a series of smaller subangles.
2. Discussion of the Prior Art
Heretofore, software has been employed in an iterative process to develop the sine function from the infinite series: ##EQU1## This software infinite series approach is slow, especially as the infinite series is expanded to fulfill higher accuracy requirements.
Simple hardware look-up tables have been employed to provide the trigonometric functions in low accuracy applications. As input bits (Nin) are added to provide more accuracy, the number of address locations in the look-up table doubles according to the relationship: EQU # of locations = 2.sup.(input places) = 2.sup.Nin
An application having 20 input bits (Nin = 20) will require over 1,000,000 ROM locations. The hardware look-up technique is a great deal faster than the software infinite series technique, but is lacking in accuracy for reasonable hardware commitments.
U.S. Pat. No. 3,813,528 to Curtis Blanding entitled "High-Speed Function Generator" teaches a look-up table technique for providing trigonometric functions in which the input angle is divided into two smaller angles according to the trigonometric identity: EQU SIN(I+II) = SIN(I)COS(II) + COS(I)SIN(II)